Assignment 5

Question #1

An n-gram, n greater than or equal to 2, is a sequence of n non-whitespace characters. The n-gram frequency matrix associated with a textfile is a matrix NM indexed by the n-grams in the textfile such that the entry for n-gram x in this matrix is the total number of occurrences of x in the textfile divided by the total number of n-grams in the textfile. Given two textfiles X and Y, let the similarity score between these textfiles be defined as Sim(X, Y) = 1.0 - (Diff(X, Y)/2.0), where Diff(X,Y) is the sum over all possible n-grams of the absolute values of the differences in frequency of occurrence of each n-gram in textfiles X and Y.

Write and document a Python script tcomp5.py which takes as command-line arguments a master textfile, a value of n, and two or more comparison textfiles and prints (1) the similarity of the master textfile and each comparison textfile and (2) the name of the comparison file that is most similar to the master textfile. Your script must work on datafiles nm1.dat, nm2.dat, nm3.dat, nm4.dat, and nm5.dat to produce the output given in typescript-file tcomp5.script. Your code must implement the similarity computation using dictionaries to encode the non-zero entries in n-gram frequency matrices. You may assume that each given textfile has at least one word, i.e., no given textfile is composed entirely of whitespace characters.

Question #2

Write and document a Python script tcomp6.py which answers Question #2 in Assignment #4 using sets instead of lists to implement the similarity computation. Your script must work on datafiles tc1.dat, tc2.dat, tc3.dat, tc4.dat, tc5.dat, and tc6.dat to produce the output given in typescript-file tcomp6.script.

Hints

You may find the answer scripts for Assignment #4 of use.

Submission

Please hand in printed copies of all of your Python script files. You must also submit these files electronically using the submit-assignment command. Note that each script file must have the following comment block at the top, where the X's are replaced with the appropriate information, followed by a docstring briefly describing the program in that script. For instance, my script for Question #1 of this assignment would begin with the following comment block:

#########################################################
##  CS 2500 (Fall 2011), Assignment #5, Question #1    ##
##   Script File Name: tcomp5.py                       ##
##       Student Name: Todd Wareham                    ##
##         Login Name: harold                          ##
##              MUN #: 8008765                         ##
#########################################################

You do not have to develop your code on our CS departmental systems. However, as your code will be compiled and tested on our CS departmental systems as part of the assignment marking process, you should ensure that your code compiles and runs correctly on at least one of these systems.

Additional Notes:

• October 18, 2:05pm
  Error in Question #1 of Assignment #5 (incorrect program results in script file) fixed.

• August 15, 3:15pm
  Assignment #5 posted.

Created: August 15, 2011
Last Modified: October 18, 2011